1. Field of the Disclosure
Embodiments disclosed herein relate generally to shale shakers, shaker screens, and uses thereof. More specifically, embodiments disclosed herein relate to shakers and shaker screens including radio frequency identification tags (RFIDT's) or surface acoustic wave tags (SAWT's), readers for tags, and uses thereof.
2. Background Art
Oilfield drilling fluid, often called “mud,” serves multiple purposes in the industry. Among its many functions, the drilling mud acts as a lubricant to cool rotary drill bits and facilitate faster cutting rates. Typically, the mud is mixed at the surface and pumped downhole at high pressure to the drill bit through a bore of the drillstring. Once the mud reaches the drill bit, it exits through various nozzles and ports where it lubricates and cools the drill bit. After exiting through the nozzles, the “spent” fluid returns to the surface through an annulus formed between the drillstring and the drilled wellbore.
Furthermore, drilling mud provides a column of hydrostatic pressure, or head, to prevent “blow out” of the well being drilled. This hydrostatic pressure offsets formation pressures, thereby preventing fluids from blowing out if pressurized deposits in the formation are breeched. Two factors contributing to the hydrostatic pressure of the drilling mud column are the height (or depth) of the column (i.e., the vertical distance from the surface to the bottom of the wellbore) itself and the density (or its inverse, specific gravity) of the fluid used. Depending on the type and construction of the formation to be drilled, various weighting and lubrication agents are mixed into the drilling mud to obtain the right mixture. Typically, drilling mud weight is reported in “pounds,” short for pounds per gallon. Generally, increasing the amount of weighting agent solute dissolved in the mud base will create a heavier drilling mud. Drilling mud that is too light may not protect the formation from blow outs, and drilling mud that is too heavy may over invade the formation. Therefore, much time and consideration is spent to ensure the mud mixture is optimal. Because the mud evaluation and mixture process is time consuming and expensive, drillers and service companies prefer to reclaim the returned drilling mud and recycle it for continued use.
Another significant purpose of the drilling mud is to carry the cuttings away from the drill bit at the bottom of the borehole to the surface. As a drill bit pulverizes or scrapes the rock formation at the bottom of the borehole, small pieces of solid material are left behind. The drilling fluid exiting the nozzles at the bit acts to stir-up and carry the solid particles of rock and formation to the surface within the annulus between the drillstring and the borehole. Therefore, the fluid exiting the borehole from the annulus is a slurry of formation cuttings in drilling mud. Before the mud can be recycled and re-pumped down through nozzles of the drill bit, the cutting particulates must be removed.
One type of apparatus that removes cuttings and other solid particulates from drilling mud is commonly referred to in the industry as a “shale shaker.” A shale shaker, also known as a vibratory separator, is a vibrating sieve-like table upon which returning used drilling mud is deposited and through which drilling mud containing substantially less drill cuttings emerges. Typically, the shale shaker is an angled table with a generally perforated filter screen bottom. Returning drilling mud is deposited at the top of the shale shaker. As the drilling mud travels along the incline toward the lower end, the fluid falls through the perforations to a reservoir below, thereby leaving the solid particulate material behind. The combination of the angle of inclination with the vibrating action of the shale shaker table enables the solid particles left behind to flow until they fall off the end of the shaker table. Preferably, the amount of vibration and the angle of inclination of the shale shaker table are adjustable to accommodate various drilling mud flow rates and particulate percentages in the drilling mud. After the fluid passes through the perforated bottom of the shale shaker, it may either return to service in the borehole immediately, be stored for measurement and evaluation, or pass through an additional piece of equipment (e.g., a drying shaker, a centrifuge, or a smaller sized shale shaker) to remove smaller cuttings and/or particulate matter.
Because shale shakers are typically in continuous use, repair operations, and associated downtimes, need to be minimized as much as possible. Often, the filter screens of shale shakers, through which the solids are separated from the drilling mud, wear out over time and subsequently require replacement. Therefore, shale shaker assemblies (i.e., filter screens and screen frames) are typically constructed to be easily removable and quickly replaceable. Generally, through the loosening of several bolts or wedges, the screen assembly may be lifted out of the shaker and replaced within a matter of minutes. While there are numerous styles and sizes of screen assemblies and filter screens, they generally follow similar design. Typically, screen assemblies include a perforated plate base upon which a wire mesh, or other perforated filter overlay, is positioned. The perforated plate base generally provides structural support and allows the passage of fluids therethrough, while the wire mesh overlay defines the largest solid particle capable of passing therethrough. While many perforated plate bases are flat or slightly arched, it should be understood that perforated plate bases having a plurality of corrugated or pyramid-shaped channels extending thereacross may be used instead. The pyramid-shaped channels may provide additional surface area for the fluid-solid separation process to take place while guiding solids along their length toward the end of the shaker.
A typical screen assembly includes a plurality of hold-down apertures at opposite ends of the filter screen. These apertures, preferably located at the ends of the screen assembly that will abut walls of the shale shaker, allow hold down retainers of the shale shaker to grip and secure the screen assembly in place. However, because of their proximity to the working surface of the screen assembly, the hold-down apertures must be covered to prevent solids in the returning drilling fluid from bypassing the filter mesh through the hold-down apertures. To prevent such bypass, an end cap assembly is placed over each end of the screen assemblies to cover the hold-down apertures. Presently, these caps are constructed by extending a metal cover over the hold down apertures and attaching a wiper seal thereto to contact an adjacent wall of the shale shaker. Furthermore, epoxy plugs are set in each end of the end cap to prevent fluids from communicating with the hold-down apertures through the sides of the end cap.
Typically, screen assemblies used with shale shakers are placed in a generally horizontal fashion on a substantially horizontal bed or support structure located within a basket in the shaker. The screens themselves may be flat, nearly flat, corrugated, depressed, and/or contain raised surfaces. The basket in which the screen assemblies are mounted may be inclined towards a discharge end of the shale shaker. The shale shaker imparts a rapidly reciprocating motion to the basket and the screen assemblies. Drilling mud, from which particles are to be separated, is poured onto a back end of the vibrating screen. The drilling mud generally flows toward the discharge end of the basket. Large particles that are unable to pass through the screen remain on top of the screen, and move toward the discharge end of the basket where they are collected. Smaller particles and fluid pass through the screen and collect in a bed, receptacle, or pan therebeneath.
In some shale shakers, a fine screen cloth is used with the vibrating screen assembly. The screen assembly may have two or more overlying layers of screen cloth or mesh. Layers of cloth or mesh may be bonded together and placed over a support, multiple supports, a perforated plate, or an apertured plate. The frame of the vibrating screen assembly is resiliently suspended or mounted upon a support, and is caused to vibrate by a vibrating mechanism (e.g., an unbalanced weight on a rotating shaft connected to the frame). Each screen assembly may be vibrated to create a flow of trapped solids on top surfaces of the screen for removal and disposal thereof The fineness or coarseness of the mesh of a screen may vary depending upon mud flow rate and the size of the solids to be removed.
As described above, the type of solids to be separated may change throughout the drilling process. Depending on the type and construction of the formation to be drilled, the solids encountered may change in composition, size, and density. As a result, the flow of the drilling fluid through and across a screen may change due to composition, tackiness, size, and other spent drilling fluid properties known to those skilled in the art. Similarly, as a shaker screen wears, flow and separation of solids through and across the screen may change.
U.S. Patent Application Publication Nos. 20060243643 and 20060108113 discloses shale shakers and shaker screen assemblies having radio frequency identification tags (RFIDT's) or surface acoustic wave tags (SAWT's) (collectively referred to herein as “tags”) disposed thereon. The tags may be removably attached to a portion of the shaker screen frame, such as a recess formed in a frame member, and may be used for purposes including relaying screen information and inventory control. The tags may also be used by a control system to determine whether a particular screen assembly is suitable for use on a particular shaker. If a screen assembly unsuitable for use is installed on a shaker, the control system can automatically shut down the shaker.
Disposing a tag on a screen frame, especially removably disposing tags on shaker screen frames, may result in an undesired level of maintenance with respect to the tags. Due to the vibratory nature of the shakers, vibrations may result in failure of the attachment, encasement, tape, or protective covering used to hold the tag to the screen frame. These failures may result in detachment of a tag, tag failure, or the exposure of the tags to fluids and chemicals during operation of the shaker.
Accordingly, there exists a need for shakers and screen frames that may allow for improved separations and separation control throughout the drilling process. There also exists a need for tagged screen assemblies that may withstand the rigors of a vibratory separator.